The OS/390 mainframe operating system is structured around the concepts of address space and task. Roughly speaking, a single address space corresponds to a single application and corresponds more or less to a process in other operating systems. Within an address space, a number of tasks may be generated and execute concurrently; this corresponds roughly to the concept of multithreading. Two data structures are key to managing this task structure. An address space control block (ASCB) contains information about an address space needed by OS/390 whether or not that address space is executing. Information in the ASCB includes dispatching priority, real and virtual memory allocated to this address space, the number of ready tasks in this address space, and whether each is swapped out. A task control block (TCB) represents a user program in execution. It contains information needed for managing a task within an address space, including processor status information, pointers to programs that are part of this task, and task execution state. ASCBs are global structures maintained in system memory, while TCBs are local structures maintained within their address space. What is the advantage of splitting the control information into global and local portions? OS2e-155